The present invention relates to a method and a device for cementing a well or a pipe, for example a casing, having a portion to be treated so as to make it leaktight, in particular to be repaired and/or plugged.
It applies more particularly, but not necessarily, to the field of oil production.
The casing is a metal tube which lines the interior of the oil well over a considerable length.
As an indication, this length is for example between 2000 and 4500 meters, whereas its internal diameter is between 120 and 200 millimeters.
In the lower part, the casing is perforated at the level of the deposit(s) that it passes through, so as to allow the passage of oil or a gaseous hydrocarbon.
Located in the upper part of the well is the wellhead, which is equipped with various systems, in particular for protection, suspension and sealing purposes.
Over a considerable length of the upper part of the well, for example between 1500 and 4000 meters, the casing is provided internally with completion equipment comprising a tube and various devices serving for exploitation of the well, such as temporary plugs and safety valves for example.
Over time, a portion of the wall of the casing may have to be sealed, in particular if has deteriorated, for example due to premature wear and/or cracking, or when the perforations intended for the passage of oil have to be plugged, in particular because the deposit has been depleted in this zone and undesirable fluid products (in particular water or gas) risk passing through the wall of the casing and penetrating into the latter.
For this purpose, said portion is treated by coating it internally with a protective material, in particular a cement, a gel or a composite material based on polymerisable resin.
In order to carry out this treatment, two different techniques may be used:                either the completion equipment is removed beforehand and it is then possible to gain direct access to the portion of the casing to be treated,        or the tools and the material used for cementing purposes are passed through the completion equipment.        
The first technique is time-consuming and expensive and may cause exploitation problems, in particular due to the fact that it is necessary to completely neutralise the well prior to any intervention.
The second technique is complicated, expensive and can be used only in a certain limited number of configurations, due to the fact that the completion equipment generally has a much smaller diameter than that of the lower zone of the casing in which the portion to be treated is located.
In particular, the installation of a cement coating is generally not possible using this technique.
The invention aims to overcome these difficulties by proposing a method and a device which make it possible to cement the lower zone of the casing while passing through the completion equipment of smaller diameter.
The invention can be applied not only to a casing as described above, but also to any hollow well in the ground or to any pipe, buried or otherwise, and for this reason the description and the claims which will follow refer to the cementing of a well or a pipe, the latter being able to be a casing or any other conduit, vertical, horizontal or oblique.